Advances in video codecs, such as MPEG-4/AVC use motion compensated prediction for inter coding. A decoder expects a motion vector for a specific block size and location. The motion vector pinpoints a location in the reference image (the previously coded image) which constructs the prediction for the current block. If the location appointed by the motion vector is not on the image grid (e.g. a fractional-pel), interpolation of the sample values is performed. Various fixed and adaptive interpolation techniques have been proposed. The resolution of the motion vectors is able to be arbitrary (up to 1/12th pel has been proposed).
However, interpolation is often fixed and cannot adapt to local statistics. For example, for interpolation of a value in the middle of four sample values, the average of the four is often used. Nevertheless, the actual value of the location is able to be close to one or two of locations if an edge is passing through the sampling locations. In this case, the average interpolation is not accurate.
Multi-hypothesis prediction for motion-compensated prediction allows multiple motion vectors from different reference pictures for prediction of P-pictures. The prediction P of a block is constructed from N prediction blocks, each appointed by a motion vector mvi, iε[1, . . . , N], where Pi is the prediction resulting from motion compensation using motion vector mvi, and wi is the weight associated with it: P=w1P1+w2P2+ . . . +wNPN. For simplicity, it is assumed wi=1/N.
Prior work only applies to P-pictures.